Lidocaine Aerosols Do Not Prevent Allergic Bronchoconstriction

Abstract

To test the effectiveness of local anesthetic aerosols in asthma, we compared the protection afforded by lidocaine and saline aerosols to bronchoconstriction provoked by inhalation of Ascaris antigen aerosols in five previously sensitized, anesthetized Basenji-Greyhound, crossbred dogs. Pulmonary resistance (RL) was determined by the method of Von Neergaard and Wirz, and blood lidocaine levels were determined by gas chromatography. Lidocaine, 4%, was administered as an aerosol for 10 minutes before challenge with Ascaris antigen and again during the 10-minute challenge with Ascaris antigen. Lidocaine aerosols frequently elicited a slight increase in RL before antigen challenge, whereas saline aerosols did not alter RL. Despite a large dose (approximately 10 mg/kg), which produced blood levels of 0.6 to 3.3 micrograms/ml, lidocaine afforded no protection against antigen challenge: RL increased from a control mean of 4.2 +/- 1.7 (SEM) cm H2O/liters/sec to 26.9 +/- 9.3 after challenge in lidocaine-treated dogs, and from 2.9 +/- 0.6 to 22.8 +/- 5.1 in saline-treated dogs. In contrast, lidocaine aerosols prevented the 7-fold increase in RL elicited by challenge with citric acid aerosols, demonstrating an adequate block of irritant reflexes. The failure of lidocaine aerosols to protect against antigen-induced bronchoconstriction indicates that the concentrations achieved in lung by this route are inadequate to relax smooth muscle directly.